I. Field of The Invention
The present invention relates in general to thermoregulators and, in particular, to thermostatic mixing valves for adjustable mixing of fluids.
II. Description of The Relevant Art
As is known to those skilled in the art to which the present invention pertains, there are devices, commonly called faucets, which are mixing valves for mixing hot and cold water in bathroom, kitchen and other facilities. Such devices usually comprise a cold water inlet, a hot water inlet, a mixing chamber and one or more valves to control water flow into the chamber.
The purpose of such mixing valves is to maintain both stable temperature and flow of the outcoming water. The process of manual temperature adjustment takes several seconds, even for a well-designed mixing valve if the temperatures and the pressures in the pipelines to both the cold and hot water inlets are stable, it is possible to adjust water temperature to a desired value after several attempts. The temperature of the outcoming water will stay stable while both the pressure and the temperature of the water in both the hot and cold inlets do not change. Frequently, however, the pressure and the temperature of the water in the inlets change depending on the load on the pipelines and a number of other conditions. Thus, a simple mixing faucet does not provide temperature stability for the outcoming water.
There are a number of technical solutions which can improve stabilization of the temperature of the outcoming water. One example is the thermostatic mixing valve which somewhat ameliorates the problem. In a thermostatic mixing valve, such as is shown in U.S. Pat. Nos. 5,108,032, 5,110,044 and 5,203,496, the relatively hot and cold fluid flows are controlled by a valve which is set by a thermally responsive element. If there is a drop in the cold water pressure, this will result in a temperature increase of the mixed fluid which will, accordingly, expand the thermally responsive element. Consequently, altering the setting of the valve decreases the hot fluid flow and increases the cold fluid flow, while still at reduced pressure, that enters the valve. Eventually, equilibrium conditions will exist with the thermal element at its new expanded condition and the valve settings. However, the new expanded condition of the thermal element corresponds with the new temperature variations but cannot provide stable temperature.
In order to improve system performance, some mixing valves (U.S. Pat. No. 5,1810,737) are designed to equalize pressures in both inlets and then stabilize the temperature. However, besides the design of such pressure equalizing valves being complicated, they are still affected by any temperature changes of the incoming fluids in the inlets. Consequently, these pressure equalizing valves cannot maintain a stable temperature.
It is thus, seen that none of the devices described above has the capability to set the temperature of the mixed water to a pre-defined known value.
Another approach to temperature control is to employ the use of a degenerative feedback device. Such a device, usually, comprises: (1) a hot water inlet, (2) a cold water inlet, (3) a mixing chamber, (4) a valve controlled by a stepper or other motor, (5) a temperature sensor, (6) an electric unit for comparing a signal from the temperature sensor with a reference signal, and (7) a motor control for making the difference in the signals as low as possible. Such devices have sophisticated electronics, often including both a microprocessor and an electrical power supply. However, the devices require safety protection against the potential of electrical shock. Also, these devices need protection against the occurrence of power loss, in order to avoid the possibility of the temperature of the mixed water running out of control. For these reasons, these devices are expensive and inapplicable in a household.
It is to be appreciated that no known device is capable of setting and maintaining the desired temperature of the fluid with low temperature fluctuations and based on an inexpensive design.